After tampering with Sheldon's Arctic-expedition data, the guys follow him back to Texas, which threatens Leonard's chances for romance with Penny.

Penny and Leonard try to recover from an awkward hookup; Howard and Sheldon make a high-stakes bet.

Howard and Raj hit a Goth nightclub to meet women; Sheldon tries chocolate-based behavior modification on Penny.

Raj faces deportation if he does not find a job; Leonard and Penny deal with Howard as a third wheel.

Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Penny to set him up with one of her friends.

Sheldon teaches Leonard how to understand football; a kite-fighting incident threatens Howard and Raj's friendship.

Sheldon tries to make peace when Leonard and Penny get into an argument.

Penny is forced to rely on Sheldon when she is injured while Howard, Leonard and Raj are away.

After being humiliated on the radio, Sheldon vows to destroy Kripke; Wolowitz tries to not ruin his new relationship with Bernadette.

Sheldon tries to help Penny understand Leonard's work; Wolowitz gets jealous when Leonard starts hanging out with his new girlfriend.

Leonard is horrified when his mother (Christine Baranski) visits.

Sheldon and Koothrappali attend a university mixer; Leonard discovers that Penny believes in psychics.

After their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

Sheldon tries to figure out the answer to a physics problem by working with Penny.

Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.

Sheldon ends up in traffic court after getting a ticket because of Penny.

When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.

Sheldon's stage fright stands between him and a coveted award.

Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.

Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.

Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.

Leonard tells Penny about how he met Sheldon and what happened to the elevator.

Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.

Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

When Sheldon searches for an alternative to human companionship, the guys become concerned.

An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.

Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.

While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Sheldon ends up in traffic court after getting a ticket because of Penny.

When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.

Sheldon's stage fright stands between him and a coveted award.

Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.

Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.

Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.

Leonard tells Penny about how he met Sheldon and what happened to the elevator.

Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.

Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

When Sheldon searches for an alternative to human companionship, the guys become concerned.

An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.

Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.

While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Sheldon ends up in traffic court after getting a ticket because of Penny.

When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.

Sheldon's stage fright stands between him and a coveted award.

Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.

Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.

Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.

Leonard tells Penny about how he met Sheldon and what happened to the elevator.

Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.

Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

When Sheldon searches for an alternative to human companionship, the guys become concerned.

An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.

Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.

While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.

The guys try to bond with Penny's new boyfriend through a costume contest.

Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.

Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.

Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.

A wealthy donor makes Leonard question what he is willing to do for science.

Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.

Sheldon is upset when he realizes Leonard is the center of their group of friends.

Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.

The guys try to figure out who hacked Sheldon's online-game account.

Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.

Priya dissects the roommate agreement; the ladies take Sheldon dancing.

Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.

Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.

Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.

Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.

The guys try to bond with Penny's new boyfriend through a costume contest.

Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.

Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.

Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.

A wealthy donor makes Leonard question what he is willing to do for science.

Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.

Sheldon is upset when he realizes Leonard is the center of their group of friends.

Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.

The guys try to figure out who hacked Sheldon's online-game account.

Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.

Priya dissects the roommate agreement; the ladies take Sheldon dancing.

Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.

Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.

Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.

Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.

The guys try to bond with Penny's new boyfriend through a costume contest.

Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.

Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.

Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.

A wealthy donor makes Leonard question what he is willing to do for science.

Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.

Sheldon is upset when he realizes Leonard is the center of their group of friends.

Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.

The guys try to figure out who hacked Sheldon's online-game account.

Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.

Priya dissects the roommate agreement; the ladies take Sheldon dancing.

Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.

Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.

Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.

Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.

Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.

Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.

Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.

Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.

Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.

An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.

Amy is devastated when Penny and Bernadette shop for wedding dresses without her.

Leonard and Penny spend time alone; Sheldon tries to face his fear of birds.

Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.

Leonard must face the bully who targeted him in high school; Penny confronts her past actions.

Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.

Everything could change when Leonard spontaneously invites Penny to a romantic dinner.

Penny and Leonard experiment with their new relationship; Raj forms a bond with his phone's virtual assistant.

Leonard starts to reconsider his friendship with Sheldon; Wolowitz tries to choose his astronaut nickname.

Sheldon goes to work with Amy in her neurobiology lab when the university forces him to take a vacation; Bernadette asks Howard to sign a pre-nup.

Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.

Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.

Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.

Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.

Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.

Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.

An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.

Amy is devastated when Penny and Bernadette shop for wedding dresses without her.

Leonard and Penny spend time alone; Sheldon tries to face his fear of birds.

Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.

Leonard must face the bully who targeted him in high school; Penny confronts her past actions.

Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.

Everything could change when Leonard spontaneously invites Penny to a romantic dinner.

Penny and Leonard experiment with their new relationship; Raj forms a bond with his phone's virtual assistant.

Leonard starts to reconsider his friendship with Sheldon; Wolowitz tries to choose his astronaut nickname.

Sheldon goes to work with Amy in her neurobiology lab when the university forces him to take a vacation; Bernadette asks Howard to sign a pre-nup.

Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.

Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.

Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.

Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.

Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.

Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.

An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.

Amy is devastated when Penny and Bernadette shop for wedding dresses without her.

Leonard and Penny spend time alone; Sheldon tries to face his fear of birds.

Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.

Leonard must face the bully who targeted him in high school; Penny confronts her past actions.

Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.

Everything could change when Leonard spontaneously invites Penny to a romantic dinner.

Penny and Leonard experiment with their new relationship; Raj forms a bond with his phone's virtual assistant.

Leonard starts to reconsider his friendship with Sheldon; Wolowitz tries to choose his astronaut nickname.

Sheldon goes to work with Amy in her neurobiology lab when the university forces him to take a vacation; Bernadette asks Howard to sign a pre-nup.

Sheldon and his nemesis, Kripke, compete for a corner office; Penny feels uncomfortable after receiving a gift from Amy.

Sheldon's routine is turned upside down when his barber gets sick; Wolowitz questions his decision to go into space.

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party; he gets a lesson from Penny and Amy.

When Penny buys Leonard and Sheldon "Star Trek" collectibles, Sheldon finds himself haunted by Mr. Spock; after a blind date, Raj believes he has met his future wife.

When Stephen Hawking comes to lecture at the university for a week, Wolowitz is given the task of maintaining his wheelchair, making Sheldon green with envy.

Knowledge of Howard's sexual history makes Bernadette reconsider their future together.

Wedding plans are jeopardized when NASA reschedules Howard's mission; Leonard says something in the bedroom that surprises Penny.

The gang tries to help Wolowitz and Bernadette get married before the space launch.

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on in space by the other astronauts.

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

Sheldon and his nemesis, Kripke, compete for a corner office; Penny feels uncomfortable after receiving a gift from Amy.

Sheldon's routine is turned upside down when his barber gets sick; Wolowitz questions his decision to go into space.

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party; he gets a lesson from Penny and Amy.

When Penny buys Leonard and Sheldon "Star Trek" collectibles, Sheldon finds himself haunted by Mr. Spock; after a blind date, Raj believes he has met his future wife.

When Stephen Hawking comes to lecture at the university for a week, Wolowitz is given the task of maintaining his wheelchair, making Sheldon green with envy.

Knowledge of Howard's sexual history makes Bernadette reconsider their future together.

Wedding plans are jeopardized when NASA reschedules Howard's mission; Leonard says something in the bedroom that surprises Penny.

The gang tries to help Wolowitz and Bernadette get married before the space launch.

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on in space by the other astronauts.

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

Sheldon and his nemesis, Kripke, compete for a corner office; Penny feels uncomfortable after receiving a gift from Amy.

Sheldon's routine is turned upside down when his barber gets sick; Wolowitz questions his decision to go into space.

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party; he gets a lesson from Penny and Amy.

When Penny buys Leonard and Sheldon "Star Trek" collectibles, Sheldon finds himself haunted by Mr. Spock; after a blind date, Raj believes he has met his future wife.

When Stephen Hawking comes to lecture at the university for a week, Wolowitz is given the task of maintaining his wheelchair, making Sheldon green with envy.

Knowledge of Howard's sexual history makes Bernadette reconsider their future together.

Wedding plans are jeopardized when NASA reschedules Howard's mission; Leonard says something in the bedroom that surprises Penny.

The gang tries to help Wolowitz and Bernadette get married before the space launch.

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on in space by the other astronauts.

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.

Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.

The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.

Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.

Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.

Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.

When Leonard receives an exciting opportunity to work overseas, Penny and Sheldon are thrown for a loop.

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.

Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.

The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.

Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.

Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.

Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.

When Leonard receives an exciting opportunity to work overseas, Penny and Sheldon are thrown for a loop.

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.

Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.

The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.

Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.

Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.

Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.

When Leonard receives an exciting opportunity to work overseas, Penny and Sheldon are thrown for a loop.

Sheldon and Penny share secrets while Leonard is away; Wolowitz helps Raj get over his ex.

Leonard and Sheldon's friendship is tested; Wolowitz's relationship with his mom causes a threat to his masculinity.

Raj designs a scavenger hunt that brings out the best - and the worst - in the whole gang.

Sheldon wants revenge after Amy ruins one of his favorite films; Leonard finds a way to get Penny to do anything; Stuart and Raj make online dating profiles.

Sheldon and Amy's relationship is tested when she takes a job at his university; a fight with Bernadette leaves Howard sleeping on Raj's couch.

Sheldon's latest scientific breakthrough leaves him feeling like a fraud; a romantic gesture between Howard and Bernadette causes Penny to up her game with Leonard.

When Professor Proton asks Leonard for help with an experiment, Sheldon retaliates by befriending Proton's rival, Bill Nye.

When a mistake comes to light, Sheldon makes Leonard walk a mile in his shoes; Penny decides to confront Raj's ex.

When the gang decides to spend Thanksgiving at Mrs. Wolowitz's house, Sheldon protests; Leonard and Penny deal with an error from her past.

Amy and Leonard try to help Sheldon deal with his shame; Raj stays with Bernadette and Howard for a week.

While Sheldon is in Texas, the rest of the gang realize how much he has changed their lives as they decorate the apartment Christmas tree.

As Leonard tries to help Penny with a disappointment, Penny asks him a bold question about their relationship; Sheldon wants to learn how to be funny.

Sheldon must learn how to relax when he is forced to take a vacation; Leonard tries to support Penny when she quits her job; Bernadette needs to replace one of Stuart's comic books.

Unable to get Comic-Con tickets, Sheldon tries to hold his own convention and ends up spending a wild evening with James Earl Jones; the ladies try to act maturely.

Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet.

When Leonard buys a dining room table, Sheldon re-evaluates the changes in his life; Bernadette is torn when Wolowitz gets the chance to go back to space.

Sheldon and Penny share secrets while Leonard is away; Wolowitz helps Raj get over his ex.

Leonard and Sheldon's friendship is tested; Wolowitz's relationship with his mom causes a threat to his masculinity.

Raj designs a scavenger hunt that brings out the best - and the worst - in the whole gang.

Sheldon wants revenge after Amy ruins one of his favorite films; Leonard finds a way to get Penny to do anything; Stuart and Raj make online dating profiles.

Sheldon and Amy's relationship is tested when she takes a job at his university; a fight with Bernadette leaves Howard sleeping on Raj's couch.

Sheldon's latest scientific breakthrough leaves him feeling like a fraud; a romantic gesture between Howard and Bernadette causes Penny to up her game with Leonard.

When Professor Proton asks Leonard for help with an experiment, Sheldon retaliates by befriending Proton's rival, Bill Nye.

When a mistake comes to light, Sheldon makes Leonard walk a mile in his shoes; Penny decides to confront Raj's ex.

When the gang decides to spend Thanksgiving at Mrs. Wolowitz's house, Sheldon protests; Leonard and Penny deal with an error from her past.

Amy and Leonard try to help Sheldon deal with his shame; Raj stays with Bernadette and Howard for a week.

While Sheldon is in Texas, the rest of the gang realize how much he has changed their lives as they decorate the apartment Christmas tree.

As Leonard tries to help Penny with a disappointment, Penny asks him a bold question about their relationship; Sheldon wants to learn how to be funny.

Sheldon must learn how to relax when he is forced to take a vacation; Leonard tries to support Penny when she quits her job; Bernadette needs to replace one of Stuart's comic books.

Unable to get Comic-Con tickets, Sheldon tries to hold his own convention and ends up spending a wild evening with James Earl Jones; the ladies try to act maturely.

Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet.

When Leonard buys a dining room table, Sheldon re-evaluates the changes in his life; Bernadette is torn when Wolowitz gets the chance to go back to space.

Sheldon and Penny share secrets while Leonard is away; Wolowitz helps Raj get over his ex.

Leonard and Sheldon's friendship is tested; Wolowitz's relationship with his mom causes a threat to his masculinity.

Raj designs a scavenger hunt that brings out the best - and the worst - in the whole gang.

Sheldon wants revenge after Amy ruins one of his favorite films; Leonard finds a way to get Penny to do anything; Stuart and Raj make online dating profiles.

Sheldon and Amy's relationship is tested when she takes a job at his university; a fight with Bernadette leaves Howard sleeping on Raj's couch.

Sheldon's latest scientific breakthrough leaves him feeling like a fraud; a romantic gesture between Howard and Bernadette causes Penny to up her game with Leonard.

When Professor Proton asks Leonard for help with an experiment, Sheldon retaliates by befriending Proton's rival, Bill Nye.

When a mistake comes to light, Sheldon makes Leonard walk a mile in his shoes; Penny decides to confront Raj's ex.

When the gang decides to spend Thanksgiving at Mrs. Wolowitz's house, Sheldon protests; Leonard and Penny deal with an error from her past.

Amy and Leonard try to help Sheldon deal with his shame; Raj stays with Bernadette and Howard for a week.

While Sheldon is in Texas, the rest of the gang realize how much he has changed their lives as they decorate the apartment Christmas tree.

As Leonard tries to help Penny with a disappointment, Penny asks him a bold question about their relationship; Sheldon wants to learn how to be funny.

Sheldon must learn how to relax when he is forced to take a vacation; Leonard tries to support Penny when she quits her job; Bernadette needs to replace one of Stuart's comic books.

Unable to get Comic-Con tickets, Sheldon tries to hold his own convention and ends up spending a wild evening with James Earl Jones; the ladies try to act maturely.

Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet.

When Leonard buys a dining room table, Sheldon re-evaluates the changes in his life; Bernadette is torn when Wolowitz gets the chance to go back to space.

Bernadette tries to negotiate peace between Sheldon and Wolowitz; Penny receives an embarrassing offer; Raj wants Amy to write to a woman on his behalf.

Sheldon is faced with a new reality when he visits his mom in Houston; a murder mystery party starts arguments.

Raj struggles with guilt when he dates two women at once; Penny has a chance to play a part in a cheesy movie; Sheldon is torn between two gaming systems.

Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.

Sheldon gives spontaneity a try, which causes unexpected friction for Penny, Bernadette and Amy; Raj asks Howard for help with preparation for a date with Emily.

Professor Proton (Bob Newhart) helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.

A bad day compels Penny to re-evaluate her choices - including Leonard; Bernadette and Howard must care for Mrs. Wolowitz; Sheldon gives Raj advice on relationships.

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette's company; Stuart's relationship with Mrs. Wolowitz disturbs Howard.

When Sheldon must teach a class, Howard decides to take it; Amy takes advantage of the tension between Penny and Bernadette.

Wolowitz feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game; Penny and Leonard want to prove Sheldon wrong after he says he and Amy are the better couple.

Raj's honesty comes back to haunt him when his new girlfriend is unfriendly to Penny; the guys think about becoming part owners in Stuart's store.

During their weekend in Las Vegas, Bernadette and Amy accuse Penny of being a buzz kill; the guys try to invent the next big thing.

Raj and Sheldon try to simulate a dark-matter research expedition; after a fight about money, Penny and Leonard turn to Bernadette and Wolowitz for advice.

The guys try to help when Penny is faced with an awkward dilemma at work; Bernadette and Amy discuss sexuality and female scientists.

Sheldon feels pressured to participate in romantic traditions when the gang re-creates a high-school prom on the roof.

Bernadette tries to negotiate peace between Sheldon and Wolowitz; Penny receives an embarrassing offer; Raj wants Amy to write to a woman on his behalf.

Sheldon is faced with a new reality when he visits his mom in Houston; a murder mystery party starts arguments.

Raj struggles with guilt when he dates two women at once; Penny has a chance to play a part in a cheesy movie; Sheldon is torn between two gaming systems.

Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.

Sheldon gives spontaneity a try, which causes unexpected friction for Penny, Bernadette and Amy; Raj asks Howard for help with preparation for a date with Emily.

Professor Proton (Bob Newhart) helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.

A bad day compels Penny to re-evaluate her choices - including Leonard; Bernadette and Howard must care for Mrs. Wolowitz; Sheldon gives Raj advice on relationships.

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette's company; Stuart's relationship with Mrs. Wolowitz disturbs Howard.

When Sheldon must teach a class, Howard decides to take it; Amy takes advantage of the tension between Penny and Bernadette.

Wolowitz feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game; Penny and Leonard want to prove Sheldon wrong after he says he and Amy are the better couple.

Raj's honesty comes back to haunt him when his new girlfriend is unfriendly to Penny; the guys think about becoming part owners in Stuart's store.

During their weekend in Las Vegas, Bernadette and Amy accuse Penny of being a buzz kill; the guys try to invent the next big thing.

Raj and Sheldon try to simulate a dark-matter research expedition; after a fight about money, Penny and Leonard turn to Bernadette and Wolowitz for advice.

The guys try to help when Penny is faced with an awkward dilemma at work; Bernadette and Amy discuss sexuality and female scientists.

Sheldon feels pressured to participate in romantic traditions when the gang re-creates a high-school prom on the roof.

Bernadette tries to negotiate peace between Sheldon and Wolowitz; Penny receives an embarrassing offer; Raj wants Amy to write to a woman on his behalf.

Sheldon is faced with a new reality when he visits his mom in Houston; a murder mystery party starts arguments.

Raj struggles with guilt when he dates two women at once; Penny has a chance to play a part in a cheesy movie; Sheldon is torn between two gaming systems.

Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.

Sheldon gives spontaneity a try, which causes unexpected friction for Penny, Bernadette and Amy; Raj asks Howard for help with preparation for a date with Emily.

Professor Proton (Bob Newhart) helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.

A bad day compels Penny to re-evaluate her choices - including Leonard; Bernadette and Howard must care for Mrs. Wolowitz; Sheldon gives Raj advice on relationships.

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette's company; Stuart's relationship with Mrs. Wolowitz disturbs Howard.

When Sheldon must teach a class, Howard decides to take it; Amy takes advantage of the tension between Penny and Bernadette.

Wolowitz feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game; Penny and Leonard want to prove Sheldon wrong after he says he and Amy are the better couple.

Raj's honesty comes back to haunt him when his new girlfriend is unfriendly to Penny; the guys think about becoming part owners in Stuart's store.

During their weekend in Las Vegas, Bernadette and Amy accuse Penny of being a buzz kill; the guys try to invent the next big thing.

Raj and Sheldon try to simulate a dark-matter research expedition; after a fight about money, Penny and Leonard turn to Bernadette and Wolowitz for advice.

The guys try to help when Penny is faced with an awkward dilemma at work; Bernadette and Amy discuss sexuality and female scientists.

Sheldon feels pressured to participate in romantic traditions when the gang re-creates a high-school prom on the roof.

Leonard has minor surgery on his nose, causing Sheldon to overreact; Bernadette and Howard work on their marriage.

Sheldon says goodbye to Fun With Flags; Howard, Leonard and Raj look through their dead professor's research; Bernadette learns her co-workers' true feelings.

Leonard and Wolowitz clash over a work emergency; Amy throws a Victorian Christmas party which Sheldon resents.

When the guys agree to do something the girls like, Sheldon and Leonard end up having a confrontation.

Sheldon asks his friends to challenge him in hope of achieving a scientific breakthrough; Wolowitz invents a game about Raj.

Sheldon and Leonard must defend themselves from an online bully's criticism after they co-publish a paper; Bernadette, Penny and Amy confront embarrassing moments during a girls night.

While the gang waits for the reopening of Stuart's comic book store Wolowitz gets some shocking news; Penny has trouble taking her own advice; Leonard and Raj think they spot Nathan Fillion at a restaurant.

Penny and Sheldon design an experiment - as a joke - to make participants fall in love; Howard and Bernadette get into trouble at the airport.

Amy finds out that Sheldon applied for a one-way mission to colonize Mars; a trip to the pet store leads to a fight; Leonard has a surprise for Penny; Raj is busted while snooping in Emily's apartment.

A magazine article only credits Sheldon in an article about a paper he co-wrote with Leonard; a blackout at Mrs. Wolowitz's results in a final dinner in her honor.

When Sheldon and Leonard are asked to speak at UC Berkeley, they take a detour in hope of meeting an idol; Raj and Amy try to settle a dispute between Howard and Bernadette with a game of pingpong.

Sheldon and Amy build a blanket fort - and come to a crossroads in their relationship; Wolowitz meets a half-brother he didn't know he had; Leonard and Penny have an argument during an appearance on Wil Wheaton's podcast.

The guys fight over what message Raj should write for NASA in case of alien contact; Penny has to decide between auditioning for a movie or keeping her pharmaceutical sales job.

Wolowitz questions his engineering skills after he and Sheldon can't get a toy drone to fly; a canceled flight puts Leonard's plans in jeopardy; Raj sets his parents against one another after he's cut off financially.

When Sheldon's and Leonard's mothers finally meet, personalities collide; Howard decides to do his share of the chores - with a little help from his friends.

While facing dramatic changes in his relationship with Amy, Sheldon pushes Penny and Leonard to choose a wedding date.

Leonard has minor surgery on his nose, causing Sheldon to overreact; Bernadette and Howard work on their marriage.

Sheldon says goodbye to Fun With Flags; Howard, Leonard and Raj look through their dead professor's research; Bernadette learns her co-workers' true feelings.

Leonard and Wolowitz clash over a work emergency; Amy throws a Victorian Christmas party which Sheldon resents.

When the guys agree to do something the girls like, Sheldon and Leonard end up having a confrontation.

Sheldon asks his friends to challenge him in hope of achieving a scientific breakthrough; Wolowitz invents a game about Raj.

Sheldon and Leonard must defend themselves from an online bully's criticism after they co-publish a paper; Bernadette, Penny and Amy confront embarrassing moments during a girls night.

While the gang waits for the reopening of Stuart's comic book store Wolowitz gets some shocking news; Penny has trouble taking her own advice; Leonard and Raj think they spot Nathan Fillion at a restaurant.

Penny and Sheldon design an experiment - as a joke - to make participants fall in love; Howard and Bernadette get into trouble at the airport.

Amy finds out that Sheldon applied for a one-way mission to colonize Mars; a trip to the pet store leads to a fight; Leonard has a surprise for Penny; Raj is busted while snooping in Emily's apartment.

A magazine article only credits Sheldon in an article about a paper he co-wrote with Leonard; a blackout at Mrs. Wolowitz's results in a final dinner in her honor.

When Sheldon and Leonard are asked to speak at UC Berkeley, they take a detour in hope of meeting an idol; Raj and Amy try to settle a dispute between Howard and Bernadette with a game of pingpong.

Sheldon and Amy build a blanket fort - and come to a crossroads in their relationship; Wolowitz meets a half-brother he didn't know he had; Leonard and Penny have an argument during an appearance on Wil Wheaton's podcast.

The guys fight over what message Raj should write for NASA in case of alien contact; Penny has to decide between auditioning for a movie or keeping her pharmaceutical sales job.

Wolowitz questions his engineering skills after he and Sheldon can't get a toy drone to fly; a canceled flight puts Leonard's plans in jeopardy; Raj sets his parents against one another after he's cut off financially.

When Sheldon's and Leonard's mothers finally meet, personalities collide; Howard decides to do his share of the chores - with a little help from his friends.

While facing dramatic changes in his relationship with Amy, Sheldon pushes Penny and Leonard to choose a wedding date.

Leonard has minor surgery on his nose, causing Sheldon to overreact; Bernadette and Howard work on their marriage.

Sheldon says goodbye to Fun With Flags; Howard, Leonard and Raj look through their dead professor's research; Bernadette learns her co-workers' true feelings.

Leonard and Wolowitz clash over a work emergency; Amy throws a Victorian Christmas party which Sheldon resents.

When the guys agree to do something the girls like, Sheldon and Leonard end up having a confrontation.

Sheldon asks his friends to challenge him in hope of achieving a scientific breakthrough; Wolowitz invents a game about Raj.

Sheldon and Leonard must defend themselves from an online bully's criticism after they co-publish a paper; Bernadette, Penny and Amy confront embarrassing moments during a girls night.

While the gang waits for the reopening of Stuart's comic book store Wolowitz gets some shocking news; Penny has trouble taking her own advice; Leonard and Raj think they spot Nathan Fillion at a restaurant.

Penny and Sheldon design an experiment - as a joke - to make participants fall in love; Howard and Bernadette get into trouble at the airport.

Amy finds out that Sheldon applied for a one-way mission to colonize Mars; a trip to the pet store leads to a fight; Leonard has a surprise for Penny; Raj is busted while snooping in Emily's apartment.

A magazine article only credits Sheldon in an article about a paper he co-wrote with Leonard; a blackout at Mrs. Wolowitz's results in a final dinner in her honor.

When Sheldon and Leonard are asked to speak at UC Berkeley, they take a detour in hope of meeting an idol; Raj and Amy try to settle a dispute between Howard and Bernadette with a game of pingpong.

Sheldon and Amy build a blanket fort - and come to a crossroads in their relationship; Wolowitz meets a half-brother he didn't know he had; Leonard and Penny have an argument during an appearance on Wil Wheaton's podcast.

The guys fight over what message Raj should write for NASA in case of alien contact; Penny has to decide between auditioning for a movie or keeping her pharmaceutical sales job.

Wolowitz questions his engineering skills after he and Sheldon can't get a toy drone to fly; a canceled flight puts Leonard's plans in jeopardy; Raj sets his parents against one another after he's cut off financially.

When Sheldon's and Leonard's mothers finally meet, personalities collide; Howard decides to do his share of the chores - with a little help from his friends.

While facing dramatic changes in his relationship with Amy, Sheldon pushes Penny and Leonard to choose a wedding date.

Sheldon struggles to understand what is going on with Amy; Penny must decide if she can get past Leonard's bad behavior.

Leonard tries to ease Penny's mind; Sheldon plans a special episode of "Fun With Flags"; Bernadette feels bad about keeping a secret.

A flat tire during Leonard's bachelor party weekend in Mexico tests the guys' skills; Penny is compelled to tell her family that she and Leonard eloped.

An impending change to his living arrangements inspires Sheldon to revert to 2003, before he met Penny and Leonard; Raj and Howard form a band.

Barry Kripke expresses interest in Amy while leading a fencing lesson for the guys; when Stuart tries to attract female customers to the store, Penny, Amy and Bernadette help out.

Leonard and Sheldon go to great lengths to secure the helium they need during a nation-wide shortage; Bernadette and Penny try to to find Amy a new man on a dating app.

Sheldon struggles to keep his emotions in check when he is interviewed for a documentary about Spock; Penny and Leonard make a surprising discovery; Wolowitz and Bernadette get into a disagreement about remodeling his childhood home.

Sheldon, Wolowitz and Koothrappali post an ad online to find a new girlfriend for Sheldon; Penny and Bernadette decide to spy when Amy is secretive about who she is dating.

Amy and Sheldon spend Thanksgiving at the aquarium - as friends; Wolowitz volunteers at the soup kitchen with Raj, Emily and Bernadette; Penny realizes that Leonard knows her better than she thought.

Sheldon has a song stuck in his head; despite their awkward date, Amy asks Dave over for dinner; Koothrappali and Wolowitz are obsessed with a fan of their band.

After dating for more than five years, Amy and Sheldon spend the night together for the first time; Leonard, Wolowitz, and Koothrappali must decide what to do with an extra movie ticket.

Leonard agrees to meet with a psychiatrist (Jane Kaczmarek) on Penny's behalf; Sheldon and Koothrappali work together on an astronomical discovery; Wolowitz and Bernadette struggle with their feelings when Stuart moves out.

After dealing with Sheldon while he was sick, Leonard, Penny and the gang attempt to treat themselves to a Sheldon-free weekend.

Sheldon's excitement about his Meemaw's visit fades when she butts heads with Amy; Raj questions his relationship with Emily after meeting someone new.

Amy and Sheldon host a Valentine's Day edition of Fun With Flags; Penny and Leonard wrestle with getting older; Howard and Bernadette make a discovery in their hot tub; Raj is torn between Emily and another woman.

The gang celebrates news of Bernadette's pregnancy by singing karaoke; Wolowitz's reaction to the pregnancy announcement worries Bernadette; Wolowitz believes he needs to make more money to support his growing family.

Sheldon struggles to understand what is going on with Amy; Penny must decide if she can get past Leonard's bad behavior.

Leonard tries to ease Penny's mind; Sheldon plans a special episode of "Fun With Flags"; Bernadette feels bad about keeping a secret.

A flat tire during Leonard's bachelor party weekend in Mexico tests the guys' skills; Penny is compelled to tell her family that she and Leonard eloped.

An impending change to his living arrangements inspires Sheldon to revert to 2003, before he met Penny and Leonard; Raj and Howard form a band.

Barry Kripke expresses interest in Amy while leading a fencing lesson for the guys; when Stuart tries to attract female customers to the store, Penny, Amy and Bernadette help out.

Leonard and Sheldon go to great lengths to secure the helium they need during a nation-wide shortage; Bernadette and Penny try to to find Amy a new man on a dating app.

Sheldon struggles to keep his emotions in check when he is interviewed for a documentary about Spock; Penny and Leonard make a surprising discovery; Wolowitz and Bernadette get into a disagreement about remodeling his childhood home.

Sheldon, Wolowitz and Koothrappali post an ad online to find a new girlfriend for Sheldon; Penny and Bernadette decide to spy when Amy is secretive about who she is dating.

Amy and Sheldon spend Thanksgiving at the aquarium - as friends; Wolowitz volunteers at the soup kitchen with Raj, Emily and Bernadette; Penny realizes that Leonard knows her better than she thought.

Sheldon has a song stuck in his head; despite their awkward date, Amy asks Dave over for dinner; Koothrappali and Wolowitz are obsessed with a fan of their band.

After dating for more than five years, Amy and Sheldon spend the night together for the first time; Leonard, Wolowitz, and Koothrappali must decide what to do with an extra movie ticket.

Leonard agrees to meet with a psychiatrist (Jane Kaczmarek) on Penny's behalf; Sheldon and Koothrappali work together on an astronomical discovery; Wolowitz and Bernadette struggle with their feelings when Stuart moves out.

After dealing with Sheldon while he was sick, Leonard, Penny and the gang attempt to treat themselves to a Sheldon-free weekend.

Sheldon's excitement about his Meemaw's visit fades when she butts heads with Amy; Raj questions his relationship with Emily after meeting someone new.

Amy and Sheldon host a Valentine's Day edition of Fun With Flags; Penny and Leonard wrestle with getting older; Howard and Bernadette make a discovery in their hot tub; Raj is torn between Emily and another woman.

The gang celebrates news of Bernadette's pregnancy by singing karaoke; Wolowitz's reaction to the pregnancy announcement worries Bernadette; Wolowitz believes he needs to make more money to support his growing family.

Sheldon struggles to understand what is going on with Amy; Penny must decide if she can get past Leonard's bad behavior.

Leonard tries to ease Penny's mind; Sheldon plans a special episode of "Fun With Flags"; Bernadette feels bad about keeping a secret.

A flat tire during Leonard's bachelor party weekend in Mexico tests the guys' skills; Penny is compelled to tell her family that she and Leonard eloped.

An impending change to his living arrangements inspires Sheldon to revert to 2003, before he met Penny and Leonard; Raj and Howard form a band.

Barry Kripke expresses interest in Amy while leading a fencing lesson for the guys; when Stuart tries to attract female customers to the store, Penny, Amy and Bernadette help out.

Leonard and Sheldon go to great lengths to secure the helium they need during a nation-wide shortage; Bernadette and Penny try to to find Amy a new man on a dating app.

Sheldon struggles to keep his emotions in check when he is interviewed for a documentary about Spock; Penny and Leonard make a surprising discovery; Wolowitz and Bernadette get into a disagreement about remodeling his childhood home.

Sheldon, Wolowitz and Koothrappali post an ad online to find a new girlfriend for Sheldon; Penny and Bernadette decide to spy when Amy is secretive about who she is dating.

Amy and Sheldon spend Thanksgiving at the aquarium - as friends; Wolowitz volunteers at the soup kitchen with Raj, Emily and Bernadette; Penny realizes that Leonard knows her better than she thought.

Sheldon has a song stuck in his head; despite their awkward date, Amy asks Dave over for dinner; Koothrappali and Wolowitz are obsessed with a fan of their band.

After dating for more than five years, Amy and Sheldon spend the night together for the first time; Leonard, Wolowitz, and Koothrappali must decide what to do with an extra movie ticket.

Leonard agrees to meet with a psychiatrist (Jane Kaczmarek) on Penny's behalf; Sheldon and Koothrappali work together on an astronomical discovery; Wolowitz and Bernadette struggle with their feelings when Stuart moves out.

After dealing with Sheldon while he was sick, Leonard, Penny and the gang attempt to treat themselves to a Sheldon-free weekend.

Sheldon's excitement about his Meemaw's visit fades when she butts heads with Amy; Raj questions his relationship with Emily after meeting someone new.

Amy and Sheldon host a Valentine's Day edition of Fun With Flags; Penny and Leonard wrestle with getting older; Howard and Bernadette make a discovery in their hot tub; Raj is torn between Emily and another woman.

The gang celebrates news of Bernadette's pregnancy by singing karaoke; Wolowitz's reaction to the pregnancy announcement worries Bernadette; Wolowitz believes he needs to make more money to support his growing family.

For the first time in nine years, the gang celebrates Sheldon's birthday - surprising him with a special guest.

Leonard, Sheldon and Wolowitz file for a patent on their new invention; Penny, Amy and Bernadette give dating advice to Koothrappali after his breakup with Emily.

Sheldon makes a surprise revelation when Amy buys him a new laptop; Leonard and Wolowitz get sold out by Koothrappali after lying to their wives to attend a movie screening.

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Koothrappali goes all out with pregnancy gifts.

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

The gang runs into Penny's old boyfriend while out at a wine bar; Bernadette spends an evening with Sheldon; Koothrappali's introduction of his new girlfriend doesn't go as planned.

Sheldon wants to go to a movie screening, so he pays Stuart to spend the day with Amy; Penny has a difficult time connecting with Leonard's visiting mother.

Leonard's recently divorced parents and Sheldon's devoutly religious mother visit; when they are contacted about their guidance system, Wolowitz and Koothrappali think the government is after them.

The group struggles through an awkward morning after Sheldon's mother and Leonard's father spend an evening together; Penny's family arrives.

Wolowitz has a meeting with Colonel Williams, a representative from the Air Force Department of Material Command.

Sheldon tries to stay awake with an energy drink as the gang races to finish its government project on time; Penny and Amy attend a gathering at Bert the Geologist's house; Koothrappali learns Bernadette's true feeling about her pregnancy.

After her apartment floods, Amy suggests that she and Sheldon move in together; Koothrappali finds out the gender of Howard and Bernadette's baby before they do.

Things do not run smoothly when Amy moves in with Sheldon, and Leonard and Penny have to intervene; Howard and Bernadette find unexpected guests at their house when they decide to cancel their vacation plans.

Penny learns there are fans of her performance in "Serial Ape-ist" when she and Leonard attend a Comic Con event; Amy hosts a brunch at Penny's apartment; Wolowitz makes an impulsive purchase.

Amy lies about repairs being made to her apartment so she can continue living with Sheldon; Leonard lets Penny decorate Sheldon's old room.

Sheldon is determined to convince Amy they should procreate; Koothrappali is reluctant to tell the gang what the new woman he's dating does for a living.

For the first time in nine years, the gang celebrates Sheldon's birthday - surprising him with a special guest.

Leonard, Sheldon and Wolowitz file for a patent on their new invention; Penny, Amy and Bernadette give dating advice to Koothrappali after his breakup with Emily.

Sheldon makes a surprise revelation when Amy buys him a new laptop; Leonard and Wolowitz get sold out by Koothrappali after lying to their wives to attend a movie screening.

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Koothrappali goes all out with pregnancy gifts.

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

The gang runs into Penny's old boyfriend while out at a wine bar; Bernadette spends an evening with Sheldon; Koothrappali's introduction of his new girlfriend doesn't go as planned.

Sheldon wants to go to a movie screening, so he pays Stuart to spend the day with Amy; Penny has a difficult time connecting with Leonard's visiting mother.

Leonard's recently divorced parents and Sheldon's devoutly religious mother visit; when they are contacted about their guidance system, Wolowitz and Koothrappali think the government is after them.

The group struggles through an awkward morning after Sheldon's mother and Leonard's father spend an evening together; Penny's family arrives.

Wolowitz has a meeting with Colonel Williams, a representative from the Air Force Department of Material Command.